The present invention relates to a penetration bomb, i.e. a bomb for use against an objective having a thick resistant wall. The term "bomb" should be construed as designating any heavy projectile which is subsonic on impact and includes glide bombs, with possibly a propulsion motor, and accelerated bombs, as well as free fall bombs, guided or not.
The invention is particularly, although not exclusively, suitable for use in the field of guided bombs for attacking precisely defined targets having considerable vertical development and accelerated bombs for attacking targets having large horizontal development, such as runways and the shielded decks of ships.
For some purposes, it is required for the bomb to completely ruin the wall and demolish it. In others, it is sufficient for it to form a crater of appreciable size and, at the same time, shake and crack the target. Penetration bombs are already known for attaining these results. They typically have a shape close to that of large-sized shells for destroying armoured targets, that is having a front ogive and a cylindrical body, with a very resistant shell and relatively small explosive content. The penetration effect is due essentially to the kinetic energy and the bombs present, with respect to shells, the drawbacks of a substantially lower speeed.
The penetration of a resistant projectile into a target is all the greater the smaller its diameter. This fact has been used more particularly in sub-caliber shells, or "arrow" shells but that approach can hardly be transposed to bombs whose speeds are much lower and whose kinetic energy is generally insufficient. It has also been suggested to fit a solid extension of small diameter forming a chisel to the front of the shell (German Pat. No. 2,036,897). Such approaches, when used on bombs, are of no substantial advantage.
It is an object of the invention to provide a penetration bomb having greatly increased efficiency for a same weight. A penetration bomb according to the invention has a body and an explosive charge. The body has a front thick-walled part and a rear part with a diameter greater than that of the front wall and a high explosive content. The front part also contains explosive but has a charge or filling coefficient (ratio of the content of explosive to total weight) very much less than that of the rear part. It is connected to the rear part by an intermediate body zone capable of transmitting to the front part the kinetic energy of the rear part at the impact.
This construction is based on a totally different approach from those previously adopted. A first crater is formed in the objective over a considerable depth by the front part due to (i) the small diameter of the front part, to which the intermediate part transmits kinetic energy. That momentum is very much greater than it would be if the rear part had the same diameter as the front part, since the mass is very much increased and (ii) the explosive charge is contained in the front part. There is mechanical damage to the wall by the front part, which forms a dart or chisel, over an area whose diameter is of about 1.4 time the diameter of the front part. When firing takes place, with a delay which will be selected depending on the characteristics of the bomb, the rear part thereof will have engaged in the area damaged by the front part so that its explosion will have maximum effect.
The front part will typically have a diameter between 0.2 and 0.8, generally 0.4 to 0.6, that of the rear part. A ratio of 0.5 will generally be close to optimum. The length of the front part and of the connecting zone will be chosen depending on the thickness of the wall of the target, at least when it is required to open a traversing breach in the wall. In practice, a length a half of the thickness to be traversed will generally be satisfactory. The filling coefficient will have a value very different in the front and rear parts, typically about 0.15 for the front part and more than 0.75 for the rear part.
The intermediate part may be designed to transmit the driving-in forces of the front part, while presenting a certain flexibility for dampening the shock of the impact: in general, an approximately conical shape having an angle at the apex between 40.degree. and 120.degree. gives satisfactory results.
The invention will be better understood from the following description of particular embodiments of the invention, given by way of examples.